Simultaneous biomass production and wastewater treatment through algal cultivation holds great potential in ameliorating nutrient pollution and eutrophication. However, it is not widely feasible in higher latitudes due to low light and temperature conditions affecting productivity and removal efficiency. These issues could potentially be offset by the mixotrophic growth of algae, as it reduces dependency on light availability. This could allow year-round operation for nutrient removal as well as biomass production, which can be used as biofuels or feedstock. The present study compares the use of local agal consortia under mixotrophic and phototrophic growth in open systems in terms of algal biomass production and nutrient removal from landfill leachate. It also explored the bacterial and algal species present in the suspended culture and associated biofilm under both modes of growth. The mixotrophic and photoautotrophic systems had similar nutrient removal rates and were highly efficient at ammonium removal (over 75% in all systems with a maximum of 99.6%). The biomass produced by the mixotrophic system was significantly higher (p<0.05) than the photoautotrophic system. The dominating algal species identified was Desmodesmus armatus in both treatments. The dominating bacteria phyla were Myxococcota, Proteobacteria and Actinobacteriota in both systems. The results indicate that mixotrophic growth produces higher biomass than photoautotrophic growth.  This implies that in the combined biomass production and wastewater treatment system utilization of mixotrophic algal growth can potentially facilitate better algal biomass production in higher latitudes than photoautotrophic growth, without loss in nutrient removal efficiency.